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Underscoring the severity of a new class of vulnerability known as clickjacking, a blogger has created a proof-of-concept game that uses a PC's video cam and microphone to secretly spy on the player.

The demo, which is available here, appears to be a simple game that tests how quickly a user can click on a series of moving targets. Behind the scenes, it combines a generic clickjacking attack with weaknesses in Adobe's Flash technology to record the player using the PC's video camera and microphone.

The proof of concept is a powerful demonstration of the spooky implications behind clickjacking. The vulnerability allows malicious webmasters to control the links visitors click on. Once lured to a booby-trapped page, a user may think he's clicking on a link that leads to Google - when in fact it takes him to a money transfer page, a banner ad that's part of a click-fraud scheme, or any other destination the attacker chooses.

It plagues every major browser, Adobe Flash, and many other browsing technologies, according to Jeremiah Grossman and Robert "RSnake" Hansen, the researchers who first sounded the clickjacking alarm. The pair was scheduled to detail the threat two weeks ago at at OWASP's AppSec 2008 Conference in New York, but canceled the talk at the request of Adobe.

The unnamed blogger behind the game said his proof of concept used Flash, but the writer went on to say that the same thing could have been achieved using Java, SilverLight, or Dynamic Hyper Text Markup Language.

In our tests, the the proof-of-concept didn't work until after we enabled our video cam in the Windows XP Device Manager. Even then, we had trouble getting it to work with Firefox, possibly because we had the NoScript extension running (but disabled). But we had no such problems when using Internet Explorer. Within 40 seconds of pressing start, there we were playing the game. The words "Your camera was clickjacked" appeared in red.

Doubting Thomases will say the answer is to disable cams, mics, and other devices that can be misused or to simply uninstall Flash. But this is to miss the larger point: Right now, unknown web masters throughout the world can control the links you click on simply by luring you to their page. The list of ways this can be abused - we're thinking government spying, corporate espionage, cyber stalking, click fraud, and even creepier things we won't bother to mention - is limited only by the imagination. Turning off the webcam may limit the damage, but it doesn't remove the underlying threat.

"I had doubts about publishing this, but, if I could have understand [sic] it so are the bad guys, so it's better to know about it," the blogger writes.

After an earlier version of this story was published, Adobe issued this advisory giving step-by-step instructions for working around the threat while a fix is pending. The company also said it expected to patch the vulnerability by the end of October. So far, makers of Internet Explorer, Firefox, Java, Safari, SilverLight and the horde of other programs vulnerable to clickjacking have been mum. ®